Fatal error while updating wordpress to 4.2

Hello,

I tried to update my website to WordPress 4.2, but when it was updating, it didn’t completely finished to process and gave this error immediately after it.

Fatal error: Cannot redeclare get_avatar_url() (previously declared in /home/deb56081/domains/joepvanderpoel.nl/public_html/wp-includes/link-template.php:3414) in /home/deb56081/domains/joepvanderpoel.nl/public_html/wp-content/themes/ninezeroseven/functions.php on line 927

I couldn’t access my wp-login.php and FTP manager anymore, so I don’t know what to do now.

Hope anyone can help me with it.
website: http://www.joepvanderpoel.nl

Thanks!